Four people were killed after a suicide bomber attacked an Afghan army bus in Kabul on Sunday. Over 22 people have been reported to be wounded, police said. This is just one more incident in a surge of violence in the Afghan capital over the past 10 days.

The Taliban have taken responsibility for the attack. This explosion is the worst since a recent assault on a popular local restaurant on January 17 that killed 21 Afghans and foreigners.

An investigation into the recent attack is already underway as reported by Hashmat Stanikzai, the chief spokesman for police in Kabul.

"The number (of victims) might change," he said.

Stanikzai said the number of wounded included several children who happened to be nearby when the blast occurred.

According to security official, the capital was hit by at least two other attacks in the last 24 hours as well.

Two people were wounded in a blast north of the city on Saturday and security sources claim that a rocket landed near the international airport on Kabul's outskirts. No casualties were listed in the rocket explosion.

The restaurant attack on earlier this month which claimed 21 lives was the worst on foreigners since the Taliban were overthrown by U.S.-led Afghan forces in 2001.

Among the foreigners killed in that attack, three United Nations staff and the International Monetary Fund's top representative in Afghanistan were killed.